State of the art propellant formulations and plastic bonded explosive compositions, at their most basic level, are composed of an oxidizer and a fuel. The composition reaction undergone by these two materials provides the energy necessary to propel the rocket, missile, shell, or bullet. Since the oxidizer fuel combination must sustain the stresses of handling, aging, storage, and use—under an extreme range of conditions, it is typically compounded in a formula consisting of a binder, plasticizer, and various solid ingredients. Ideally, all of the components in the formulation act as either oxidizers or fuels, contributing to the energy necessary for maximum propulsion performance; although in practice, certain necessary ingredients such as stabilizers and burn rate catalysts/modifiers, have little or no energy to impart to the reaction.
The performance of the propellant is directly proportional to the enthalpy release of the oxidizer and fuel ingredients as they undergo combustion, and inversely proportional to the molecular weight of the gases produced in the combustion reaction. In practice, some tradeoffs are necessary to gain the best performance from available ingredients and formulations. Aluminum, for instance, is a fuel whose combustion products are relatively high in molecular weight, and are in most cases, not gases at all, but solids. However, the enthalpy release by the combustion of aluminum is so great in proportion to anything else, which would otherwise be available as a fuel ingredient, that the metal is commonly used as a fuel in high-performance tactical and strategic rocket motor applications. Another material commonly utilized, despite some drawbacks, is the oxidizer ammonium perchlorate. This material has a high negative enthalpy of formation, limiting its energy release upon combustion, and, in addition, it produces hydrogen chloride upon combustion, a relatively high-molecular-weight toxic gas. However, ammonium perchlorate is inexpensive, easy to formulate, has very tractable ballistics and favorable burn characteristics, and so, despite its limitations, it is the state-of-the-art oxidizer for most solid propellant rocket motor formulations.
The addition of nano-sized particles as an energetic ingredient in propellant formulations, because of their small size and high surface area-to-volume ratio enables the propellant to achieve higher burning rates and impetus. Theoretically, an advantage of using aluminum particles in nano-dimensions is that they have a short ignition delay and combustion time. If the particles burn close to the propellant surface, the heat feedback rate into the propellant surface can be increased, causing an increase in the overall burn rate. However, the addition of nano-sized aluminum particles to fast burning HE (high-energy) propellants, e.g. RDX or CL-20 based propellants, did not modify the burn rate as expected. An article by Manning, et al, Effects of Nano-sized Energetic Ingredients in High Performance Solid Gun Propellants, available at the Defense Technical Information Center, Ft. Belvoir, Va., on line at: “www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA481943 May, 2008”, discloses that the addition of nano-sized aluminum particles to an HE formulation slightly decreased the propellant burn rate at pressures below 41.4 MPa, while exhibiting almost no effect on the burn rate above this pressure.
The Manning article further stated that the addition of nano-sized boron to HE propellant formulations produced the same lack of effect as did the addition of nano-sized aluminum particles. Whereas prior to the experimentation, one would have logically thought that nano-sized boron particles would enhance the burn rate of any HE propellant—considering that boron has the highest volumetric heat of oxidation of all common fuels, 137.45 kJ/cm3, a high gravimetric heat of oxidation, 58.74 kJ/gm, and a density of 2.34 gm/cm3, which is much lower than aluminum and should have increased the mass burning rate of the propellant.
Kuhl et al, Detonation of Metastable Clusters, 39th ICT Conference on Energetic Materials, June 2008, reported that polymeric nitrogen can accumulate 4 ev/atom in its N8 face-centered-cube gauche (FCC) structure, releasing energy by cluster fission: N8→4N2. Kuhl studied the locus of states in thermodynamic state space for the detonation of such a metastable polymeric nitrogen. In particular, the equilibrium isentrope, starting at the Chapman-Jouguet state, and expanding down to 1 atmosphere was calculated with the Cheetah code. Large detonation pressures (3 Mbar), temperatures (12 kilo-K) and velocities (20 km/s) are a consequence of the large heat of detonation (6.6 kilo-cal/g) for such a nitrogen cluster-based polymer. Kuhl concluded that if such metastable nitrogen cluster-based polymer could be synthesized, it would offer the potential for large increases in the energy density of materials.
Therefore there is a need in the art for a nitrided nano-sized particle that can be added to propellants to enhance the burn rates thereof, particularly such a particle incorporating a synthesized metastable nitrogen cluster based polymer that will add very significant energy upon detonation thereof.